Scientists want to learn more about how black holes distort the
universe around them, hoping to see if the leading theory
regarding black holes, Einstein's theory of general relativity,
holds up or if new concepts might be necessary. One way to see
how black holes warp space and time is by looking at clocks near
them. Cosmic versions of clocks are known as pulsars — rapidly
spinning neutron stars that regularly give off pulses of radio
waves.

Pulsar tells the tale

Astronomers have been searching for pulsars near Sagittarius A*
for the past 20 years.

Earlier this year, NASA's NuSTAR telescope helped confirm the
existence of such a pulsar apparently less than half a light-year
away from the
black hole, one that pulsates radio signals every 3.76
seconds. Scientists quickly analyzed the pulsar using the
Effelsberg Radio Observatory of the Max Planck Institute for
Radio Astronomy in Bonn, Germany.

"On our first attempt, the pulsar was not clearly visible, but
some pulsars are stubborn and require a few observations to be
detected," said study lead author Ralph Eatough, an
astrophysicist at the Max Planck Institute for Radio Astronomy in
Bonn, Germany. "The second time we looked, the pulsar had become
very active in the radio band and was very bright. I could hardly
believe that we had finally detected a pulsar in the galactic
center." [ See
a video of the pulsar and zoom in on the Milky Way's black
hole ]

Additional observations were performed in parallel and
subsequently with other radio telescopes around the world. "We
were too excited to sleep in between observations," said study
co-author Evan Keane from the Jodrell Bank Observatory in
England.

The newfound pulsar, named PSR J1745-2900, belongs to a rare kind
of pulsars known as magnetars, which only make up about 1 out of
every 500 pulsars found to date. Magnetars possess extremely
powerful magnetic fields, ones about 1,000 times stronger than
the magnetic fields of ordinary neutron
stars, or 100 trillion times the Earth's magnetic field.

The radio pulses from magnetars are highly polarized, meaning
these signals oscillate along one plane in space. This fact
helped the researchers detect a magnetic field surrounding
Sagittarius A*.

Black hole magnetic field revealed

Black holes swallow their surroundings, mainly hot ionized gas,
in a process of accretion. Magnetic fields threading within this
accretion flow can influence how this infalling gas is structured
and behaves.

"The magnetic field we measure around the black hole can regulate
the amount of matter the black hole eats and could even cause it
to spit matter out in so-called jets," Eatough told SPACE.com.
"These measurements are therefore of great importance in
understanding how supermassive black holes feed, a process that
can affect galaxy formation and evolution."

As radio signals traverse the
magnetized gas around black holes, the way they are polarized
gets twisted depending on the strength of the magnetic fields. By
analyzing radio waves from the magnetar, the researchers
discovered a relatively strong, large-scale magnetic field
pervades the area surrounding Sagittarius A*.

In the area around the pulsar, the magnetic field is about 100
times weaker than
Earth's magnetic field. However, "the field very close to the
black hole should be much stronger — a few hundred times the
Earth's magnetic field," Eatough said.

If the magnetic field generated by the infalling gas is accreted
down to the event horizon of the black hole — its point of no
return — that could help explain the radio and X-ray glow long
associated with Sagittarius A*, researchers added.

"It is amazing how much information we can extract from this
single object," said study co-author Adam Deller at the
Netherlands Institute for Radio Astronomy in Dwingeloo.

Astronomers predict there should be thousands of pulsars around
the center
of the Milky Way. Despite that, PSR J1745-2900 is the first
pulsar discovered there. "Astronomers have searched for decades
for a pulsar around the central black hole in our galaxy, without
success. This discovery is an enormous breakthrough, but it
remains a mystery why it has taken so long to find a pulsar
there," said study co-author Heino Falcke at Radboud Universiteit
Nijmegen in the Netherlands.

"It could be the environment is very dense and patchy, making it
difficult to see other pulsars," Eatough added.

The researchers cannot test the leading theory regarding black
holes using PSR J1745-2900 — they cannot measure the way it warps
space-time accurately enough, since the pulsar is slightly too
far away from Sagittarius A* and, being relatively young, its
spin is too variable. The researchers suggest pulsars that are
closer to the black hole and are older with less variable spins
could help test the theory.

"If there is a young pulsar, there should also be many older
ones. We just have to find them," said study co-author Michael
Kramer, director of the Max Planck Institute for Radio Astronomy.

The scientists detailed their findings online Aug. 14 in the
journal Nature.